In Japan, the term hikikomori is used to describe people who've become so socially withdrawn that they refuse to leave their homes for weeks and even months at a time.

For Sasami Tsukuyomi, a shut-in attempting to pass her first year of high school, it's more than just a word. Fortunately, she lives with her older brother Kamiomi, who just happens to be a teacher at the exact school Sasami is supposed to attend. With the help of her "Brother Surveillance Tool," Sasami is able to view the outside world via her computer, theoretically allowing her to readjust to interacting with people once more. In reality, it reveals her brother's interactions with the three very odd Yagami sisters, whose looks and motives are deceiving, and have various types of interest in Kamiomi. That's when things start to get really weird… Magical powers? Everything turning into chocolate? Has life via the web warped Sasami's brain, or is it the universe that's going crazy?

It looks like Sasami will have to take off her pajamas and go out into the real world to set things straight in Sasami-san@Ganbaranai!